Recently, resin made intake manifolds, instead of metals such as aluminum alloy castings, are widely adopted from the perspective of weight saving, thermal insulating properties and improvement in design flexibility for vehicle gasoline engines. However, if resin is used for the intake manifold, warpage and shrinkage are unavoidable in the molding process, and thus form accuracy of the intake manifold tends to lower compared to those of the metals.
In case of a four-cylinder engine, an intake manifold has four intake passages at a body thereof and an intake system which controls an amount or flow velocity and direction of intake air as needed. The intake system is configured so that an opening and closing valve, which is opened and closed by a shaft, is disposed in each intake passage. The opening of the opening and closing valve is controlled by an actuator for obtaining an optimal engine combustion state in accordance with the running condition of the vehicle.
In the intake system of the combustion engine disclosed in JP 2006-233907A, a cartridge of a control unit is inserted into a receiving portion with a predetermined clearance and is held via an elastic member.
In the intake system of the combustion engine disclosed in JP 2002-106370A, a notch is provided at a peripheral wall of a frame member (cartridge) of the control unit and thereby enabling the frame to elastically shrink and deform for allowing the deformation of the frame member.
However, in the invention disclosed in JP 2006-233907A, when the intake manifold is deformed due to its dimensional change caused by thermal expansion or fluid absorption, the cartridge of the control unit may be deformed via the elastic member. If the cartridge is deformed, the opening and closing valve might be accidentally locked, or bearings of the shaft might not be aligned at desired positions with high accuracy, leading to increases in sliding friction and wear of the bearings when rotating the opening and closing valve. If a clearance defined between the cartridge and the opening and closing valve is enlarged in order to prevent the locking of the opening and closing valve, a sealing performance might deteriorate at the time of closure of the opening and closing valve.
In the invention disclosed in JP 2002-106370A, the clearance defined between the frame member and the opening and closing valve should be formed to be relatively large in order to allow the deformation of the frame member, and thus deteriorating the sealing performance at the time of the closure of the opening and closing valve.
A need exists for an intake system of an internal combustion engine which is not susceptible to the drawback mentioned above.